In the steel pipe or tube (hereinafter referred to as “pipe” when deemed appropriate) manufacturing process, in order to control the manufacturing history information about steel pipes, according to conventional practice, numbers for identifying individual steel pipes have been written by hand on the steel pipes and manufacturing history information tied to the numbers written on the steel pipes has been written down on sheets of paper. However, the numbers written on the steel pipes may sometimes disappear during the conveyance of the steel pipes in each manufacturing process and hence with the above-described method, the manufacturing history information about the steel pipes may become incapable of being properly controlled. The present applicant proposed in Patent Literature 1 that a two-dimensional code indicating an identifier for identifying pipes, such as steel pipes, be carved on a pipe by means of imprinting and the like. If a two-dimensional code is carved on a pipe by means of imprinting and the like, it is possible to prevent the two-dimensional code from disappearing during the conveyance of the pipe in each manufacturing process.
In the case where such a two-dimensional code is carved on a pipe, the two-dimensional code is read out, for example, by optical read means composed of illumination means, image pickup means and the like before the pipe is caused to undergo each manufacturing process or while the pipe is being caused to undergo each manufacturing process. Next, manufacturing history information obtained in each manufacturing process and an identifier indicated by the read-out two-dimensional code are stored by being tied to each other. By performing the above-described actions, it is possible to appropriately control the manufacturing history information about pipes in each manufacturing process.
However, optimum read conditions of a two-dimensional code which enable the two-dimensional code carved on a pipe by means of imprinting and the like to be read stably and with good accuracy (for example, optimum directions for the illumination direction and image pickup direction of a two-dimensional code) have not been found out. For this reason, in some cases it was impossible to control pipe manufacturing history information in each manufacturing process properly and efficiently by using a two-dimensional code carved on a pipe by means of imprinting and the like.